Catalytic microchannel reformer

ABSTRACT

An apparatus and method for enhancing the yield and purity of hydrogen when reforming hydrocarbons is disclosed in one embodiment of the invention as including receiving a hydrocarbon feedstock fuel (e.g., methane, vaporized methanol, natural gas, vaporized diesel, etc.) and steam at a reaction zone and reacting the hydrocarbon feedstock fuel and steam in the presence of a catalyst to produce hydrogen gas. The hydrogen gas is selectively removed from the reaction zone while the reaction is occurring by selectively diffusing the hydrogen gas through a porous ceramic membrane. The selective removal of hydrogen changes the equilibrium of the reaction and increases the amount of hydrogen that is extracted from the hydrocarbon feedstock fuel.

RELATED APPLICATIONS

This application claims priority to, and the benefit of, U.S.Provisional Patent No. 60/871,398 filed on Dec. 21, 2006 and entitledCATALYTIC MICROCHANNEL REFORMER, which application is incorporated byreference.

U.S. GOVERNMENT INTEREST

This invention was made with Government support under grant numberDMI-0321692, awarded by the National Science Foundation. The Governmenthas certain rights in this invention.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to microreactors and more particularly tomicroreactors for reforming hydrocarbon fuels and generating hydrogengas.

2. Description of the Related Art

A microreactor (or microstructured reactor or microchannel reactor) is adevice in which chemical reactions are designed to take place inconfined spaces having lateral dimensions of less than 1 mm. Currently,there are major technological issues that prevent current technologyfrom meeting the needs of microreactors for generating hydrogen, syngas,or performing specialty chemical synthesis. In general, gas-phasereactions for generating hydrogen and other specialty chemicals requiremicrofabricated components that can perform under harsh operatingconditions such as high temperatures, high temperature transients, orcorrosive or erosive environments.

Current microfabrication processes (e.g., wet etching, dry etching,lithography, LIGA, etc.) are primarily applicable to silicon,photoresists, and metals. These materials readily corrode when subjectedto hot gas streams that contain corrosive ingredients such as oxygen,steam, CO₂, sulphur, and trace metals, each of which may be present whengenerating H₂ from natural gas or using gas-phase specialty chemicalsynthesis. Another important factor when generating hydrogen gas forfuel cells is the H₂ to CO ratio, since a higher ratio reduces the costof CO removal.

The few processes that are available for microfabricating ceramics areeither prohibitively expensive due to the need for very expensiveprecursor materials, such as pre-ceramic polymers, or are unable toattain the high precision required as a result of shrinkage that occursduring sintering. The shrinkage problem in particular often creates aneed for very expensive secondary machining operations. Furthermore,many high temperature gas-phase reactions require passing gas streamsover catalysts. The introduction of catalysts into silicon, metal, orsintered-ceramic-based microreactors is typically a complex multi-stepprocess that requires a high surface area (i.e., highly porous)wash-coat to be applied inside the channels of the microreactor prior tocatalyst deposition. This wash-coat is necessitated by the very lowcomponent surface area of silicon and metals. The wash-coat is typicallyeasily damaged during operation because it poorly bonds with silicon,metal or sintered ceramic. This characteristic undesirably shortens thelife of the microreactor.

In view of the foregoing, what are needed are robust ceramic materialsfor fabricating microreactors that are able to withstand hightemperatures, high temperature transients, or corrosive or erosiveenvironments and thus have excellent thermal shock resistance andthermal cycling properties. Ideally, such materials would enablefeatures to be fabricated in net-shape and net-size with very highprecision. Further needed are microreactors that increase the H₂ to COratio to reduce the cost of CO removal by secondary operations such asmembrane reactors. Further needed are microreactors to increase theamount of hydrogen that can be extracted from hydrocarbon feedstockfuels. Further needed are ceramic materials that enable cost-effectivefabrication of microreactors. Yet further needed are porous ceramicmaterials with intrinsically high surface area that can be infiltratedwith catalysts to increase hydrocarbon reformation efficiency.

SUMMARY OF THE INVENTION

Consistent with the foregoing and in accordance with the invention asembodied and broadly described herein, a method for enhancing the yieldand purity of hydrogen when reforming hydrocarbons is disclosed in oneembodiment of the invention as including receiving a hydrocarbonfeedstock fuel (e.g., methane, vaporized methanol, natural gas,vaporized diesel, etc.) and steam at a reaction zone and reacting thehydrocarbon feedstock fuel and steam in the presence of a catalyst toproduce hydrogen gas. The hydrogen gas is selectively removed from thereaction zone while the reaction is in process by selectively diffusingthe hydrogen gas through a porous ceramic membrane. The selectiveremoval of hydrogen changes the equilibrium of the reaction andincreases the amount of hydrogen that can be extracted from thehydrocarbon feedstock fuel.

In selected embodiments, the porous ceramic membrane is fabricated froma mixture of alumina powder and a phosphate-containing reagent to reactwith the alumina powder. For example, HSA-CERCANAM® provides one suchmaterial. This material is able to withstand high temperatures, hightemperature transients, and corrosive and erosive environments. Thus,this material has excellent thermal shock resistance and thermal cyclingproperties. In selected embodiments, the method further includesproviding heat to the reaction zone to react the hydrocarbon feedstockfuel and steam. This heat may be generated by combusting one or moreresidual reactants or reaction products such as hydrocarbons, hydrogengas, and carbon monoxide that are left over or are byproducts of thehydrocarbon/steam reaction.

In another aspect of the invention, a device for enhancing the yield andpurity of hydrogen when reforming hydrocarbons may include an inlet forreceiving a hydrocarbon feedstock fuel and steam. A reaction zone may beplaced in communication with the inlet to react the hydrocarbonfeedstock fuel and steam in the presence of a catalyst to producehydrogen gas. A porous ceramic membrane is provided to selectivelyremove hydrogen gas from the reaction zone while the reaction inoccurring, thereby increasing the extent of reaction between thehydrocarbon feedstock fuel and the steam and increasing the yield ofhydrogen.

In yet another aspect of the invention, a ceramic microchannel devicefor reforming a hydrocarbon fuel to produce hydrogen gas is disclosed.This ceramic microchannel device is fabricated at least in part from aceramic made be mixing alumina powder with a phosphate-containingreagent to react with the alumina powder.

In yet another aspect of the invention, a method for enhancing the yieldand purity of hydrogen when reforming hydrocarbons includes receiving ahydrocarbon feedstock fuel and steam at a reaction zone. The hydrocarbonfeedstock fuel and steam are then reacted at the reaction zone toproduce hydrogen gas. The hydrogen gas is then selectively removed fromthe reaction zone while the reaction is occurring by extracting hydrogengas or hydrogen ions from the reaction zone. In selected embodiments,the hydrogen gas is removed from the reaction zone by diffusing thehydrogen gas through a porous ceramic membrane. In other embodiments,hydrogen gas is removed from the reaction zone by conducting hydrogenions through an ionically-conductive ceramic membrane.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the advantages of the invention will be readilyunderstood, a more particular description of the invention brieflydescribed above will be rendered by reference to specific embodimentsillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through use of theaccompanying drawings in which:

FIG. 1 is a high-level schematic diagram of one embodiment of acatalytic microchannel reformer in accordance with the invention;

FIG. 2 is a high-level schematic diagram of another embodiment of acatalytic microchannel reformer in accordance with the invention;

FIG. 3 is a perspective view of one embodiment of a stack of catalyticmicrochannel reformers in accordance with the invention;

FIG. 4 is a perspective view of one embodiment of a single catalyticmicrochannel reformer in accordance with the invention;

FIG. 5 is a cutaway perspective view of the catalytic microchannelreformer of FIG. 4;

FIG. 6 is an alternative cutaway perspective view of the catalyticmicrochannel reformer of FIG. 4;

FIG. 7 is a graph showing the product gas composition in relation to theextent of reaction of a steam-methane-reforming (SMR) reaction;

FIG. 8 is a graph showing the product gas composition in relation to theextent of reaction of a water-gas-shift (WGS) reaction; and

FIG. 9 is a graph showing the extent of reaction for an SMR reactionwhere a catalyst is embedded in a high-surface-area CERCANAM® materialand a low-surface-area CERCANAM® material.

DETAILED DESCRIPTION OF THE INVENTION

It will be readily understood that the components of the presentinvention, as generally described and illustrated in the Figures herein,could be arranged and designed in a wide variety of differentconfigurations. Thus, the following more detailed description of theembodiments of the invention, as represented in the Figures, is notintended to limit the scope of the invention, as claimed, but is merelyrepresentative of certain examples of presently contemplated embodimentsin accordance with the invention. The presently described embodimentswill be best understood by reference to the drawings, wherein like partsare designated by like numerals throughout.

Referring to FIG. 1, in selected embodiments, a catalytic microchannelreformer 100 in accordance with the invention may be adapted to receivean input 102, comprising a hydrocarbon feedstock fuel and steam, at areaction zone 104. For the purposes of this description, a hydrocarbonincludes any molecule containing both hydrogen and carbon. In selectedembodiments, the reaction zone 104 may exist within one or moremicrochannels of the device 100, as will be explained in more detailhereafter. In selected embodiments, an input 102 comprising methane(CH₄) (the primary constituent in natural gas) and steam (H₂O) may beused as the inputs to the reaction zone 104. For the purposes of thisdisclosure, methane will be used as the hydrocarbon feedstock fuel. Inother embodiments, however, other hydrocarbon feedstock fuels such aspropane, methanol, diesel, or the like, may be used in place of methane.Where the feedstock fuel is a liquid, some pre-heating may be performedto vaporize the liquids prior to input to the reformer 100.

At the reaction zone 104, the reactants 102 may be heated toapproximately 650° C. to 700° C. in the presence of a catalyst, such asa nickel-based catalyst or other catalyst known in the art. The catalystwill cause the steam and methane to react to form carbon monoxide andhydrogen in accordance with the following reaction:CH₄+H₂O→CO+3H₂

This reaction is commonly referred to as steam methane reforming (SMR),which is one of the most common and least expensive methods forproducing bulk hydrogen. In selected embodiments, the reactant stream102 may be pre-heated prior to being input to the device 100 to aid thereformation process and reduce the time and amount of heat that isrequired to bring the reactants 102 to the necessary temperature.

In selected embodiments, additional hydrogen may be recovered at thereaction zone 104 using a lower temperature (550° C. to 600° C.)gas-shift reaction. This reaction may react the carbon monoxide (CO)generated above with steam to produce hydrogen gas and carbon dioxide inaccordance with the following equation:CO+H₂O→CO₂+H₂

This reaction is commonly referred to as a water-gas-shift (WGS)reaction. Both of the above reactions require steam as one of thereactants. In selected embodiments, a high steam-to-methane ratio (e.g.,2:1) may be provided in the input stream 102 to ensure that coking isminimized during the SMR and WGS reactions.

In selected embodiments, the microchannel reformer 100 may be designedsuch that the SMR and WGS reactions take place isothermally. Because themicrochannel reformer 100 may be very small (with dimensions on theorder of several inches), the small size may impose substantiallyisothermal conditions. In general, a higher temperature (generally above600° C.) favors the forward reaction in the case of SMR and the reversereaction in the case of WGS. This is one reason why these two reactionsare generally not combined in a single reactor. However, in selectedembodiments, a microchannel reformer 100 in accordance with theinvention may combine both of these reactions in a single device 100.Both of these reactions may be driven to near completion by continuouslyremoving hydrogen gas from the reaction zone 104. This may beaccomplished using a porous ceramic membrane 106 (with micro- ornano-sized pores) located adjacent to the reaction zone 104. As the SMRand WGS reactions proceed in a forward direction, hydrogen gas mayselectively diffuse through the membrane 106, creating a deficit ofproduct (hydrogen) in the reaction zone 104. This deficit may drive theSMR and WGS reactions nearer to completion. In alternative embodiments,an ionically-conductive membrane 106 may be used to selectively removehydrogen gas from the reaction zone 104 by transporting hydrogen ionsthrough the membrane 106.

For the purpose of this description, “selectively” removing hydrogenfrom the reaction zone 104 may also include removing other gaseousspecies from the reaction zone 104 by diffusion through the membrane106, although this may occur at a significantly lower diffusion rate.Thus, the term “selectively,” as used herein, does not necessarily meanexclusively removing hydrogen, but rather that the membrane 106 mayremove hydrogen gas from the reaction zone 104 at a faster rate than itremoves other gaseous species. The higher diffusion rate of hydrogen isprimarily due to hydrogen's lower molecular weight compared to othergaseous species in the reformer 100. The diffusion rate is proportionalto the square root of the molecular weight of each gas. By removinghydrogen from the reaction zone 104 faster than other gaseous species,the equilibrium of the SMR and WGS reactions may be shifted, driving thereactions nearer to completion.

As shown in FIG. 1, a product stream 108 may contain primarily H₂, butmay also include secondary gaseous species such as CO, CO₂, H₂O, andCH₄. Reactants and reaction products that do not diffuse through themembrane 106, which may include primarily CO₂ and H₂O, but may alsoinclude residual CO, H₂, and CH₄, may be conveyed to a combustion zone110. Here, the reactants and reaction products may be combusted in thepresence of air 114 to generate heat and fully oxidize the remainingreactants in accordance with the following equations:2CO+O₂→2CO₂+Heat2H₂+O₂→2H₂O+HeatCH₄+2O₂→CO₂+2H₂O+Heat

After combustion, an exhaust stream 112 containing primarily CO₂ and H₂Omay be output from the microchannel reformer 100. Ideally, themicrochannel reformer 100 will be designed such that the amount ofcombustible gases conveyed to the combustion zone 110 will produceenough heat to drive the SMR reactions in the reaction zone 104, whilestill maximizing the amount of hydrogen in the product stream 108. TableI below shows various calculations with respect to the gas compositionsat various locations in the microchannel reformer 100. The calculationsin Table I assume that the extents of reaction for both the SMR and WGSreactions stay constant through the reaction zone 104. Morespecifically, Table I shows approximate gas compositions inside thereaction zone 104 and the product zone 107 assuming that the extent ofreaction for both the SMR and WGS reactions is 0.9 and the initialsteam-to-methane ratio is 2:1.

As indicated in Table I, the diffusion rate of hydrogen is almost threetimes greater than the next closest gas. Furthermore, Table I shows thatthe gas composition in the reaction zone 104 may include about 73.1percent H₂ after the SMR and WGS reactions have progressed to nearcompletion. The H₂ concentration in the product stream 108 may increaseto about 91.4 percent after the hydrogen and other gases diffuse throughthe membrane 106. This concentration may increase to about 93.8 percentafter water is removed (e.g., condensed) from the product stream 108.The hydrogen concentration may be increased even further if the CO₂ isremoved from the product stream through a process such as compressionand liquefaction.

TABLE I Expected Gas Compositions Product Product Stream ReactionDiffusion Stream Compo- zone Gas Rate Composition - sition - MolecularComposition Relative to Wet Basis Dry Basis Gas Weight (%) H₂ (%) (%) H₂2 73.1 1.000 91.4 93.8 CH₄ 16 2.1 0.354 0.9 0.9 H₂O 18 6.0 0.333 2.5 0.0CO 28 1.9 0.267 0.6 0.6 CO₂ 44 16.9 0.213 4.5 4.6

As mentioned previously, gas-phase reactions for generating hydrogen orsyngas typically require microfabricated components that can performunder harsh operating conditions such as high temperatures, hightemperature transients, or corrosive or erosive environments. Suchmaterials should have excellent thermal shock resistance and thermalcycling properties. Further needed are materials that enable features tobe fabricated in net-shape and net-size with very high precision.

In selected embodiments in accordance with the invention, ceramicmaterials marketed under the tradename CERCANAM® may be used tofabricate all or part of the catalytic microchannel reformer 100. Theseceramic materials may be classified as either HAS-CERCANAM®, which has avery high surface area and a continuous nanopore network, or regularCERCANAM® or LSA-CERCANAM®, which is substantially the same material butis designed to have a lower surface area and thus a reduced porestructure. In general, these ceramic materials may be classified asphosphate-bonded ceramic materials. That is, each of these CERCANAM®compositions may be fabricated from ceramic powders (e.g., aluminapowder) combined with phosphate-containing reagents (e.g., phosphoricacid). The phosphate-containing reagents may react with the ceramicpowders to bond the ceramic powders together.

In selected embodiments, the pore-structure of the HSA-CERCANAM® may becreated or enhanced simply by adding a pore former to the LSA-CERCANAM®slip. CERCANAM® and similar materials are disclosed, for example, inU.S. patent application Ser. No. 11/464,476 filed on Aug. 14, 2006 andentitled PROCESS FOR MAKING CERAMIC INSULATION and U.S. patentapplication Ser. No. 11/781,125 filed on Jul. 20, 2007 and entitledMETHOD FOR JOINING CERAMIC COMPONENTS, both of which are incorporated bythis reference.

The CERCANAM® material described herein is particularly suitable forfabricating a catalytic microchannel reformer 100 in accordance with theinvention. For example, both HSA-CERCANAM® and LSA-CERCANAM® exhibitthermal stability in oxidizing and reducing environments up to 1000° C.for at least 16 hours. Thus, this material may be used to fabricate amicrochannel reformer 100 with long life and minimal componentdegradation. Furthermore, both HSA-CERCANAM® and LSA-CERCANAM® exhibitexcellent thermal shock resistance when rapidly cycled between roomtemperature and 800° C. This facilitates rapid heating or cooling of themicrochannel reformer 100 during startup or shutdown. In selectedembodiments, fuel in the microchannel reformer 100 may be spark-ignitedfor rapid heat-up to 700° C.

Another benefit of both HSA-CERCANAM® and LSA-CERCANAM® is that theseceramic materials may be microfabricated in net-shape and net-size withvery high precision. In selected embodiments, these materials may becast in various shapes and forms to fabricate monolithic components. Theunique characteristics of CERCANAM® allow it to be cast on and aroundfeatures, either sacrificial or permanent. Using sacrificial features,for example, microchannels may be incorporated internally into amonolithic CERCANAM® piece in a simple one-step process. Wherestructures include both HSA-CERCANAM® and LSA-CERCANAM®, the structuremay be fabricated in two casts, one each for HSA-CERCANAM® andLSA-CERCANAM®. The ability to fabricate CERCANAM® components usingminimal fabrication steps significantly lowers component costs.

In selected embodiments in accordance with the invention, a microchannelreformer 100 may be fabricated from both HSA-CERCANAM® and LSA-CERCANAM®compositions. For example, the cross-hatched portions 116 of thereformer 100 may be fabricated from LSA-CERCANAM® while thecross-hatched portions 118 may be fabricated from HSA-CERCANAM®. Thus,in selected embodiments, the membrane 106 may be fabricated fromHSA-CERCANAM® because it provides a material with high surface area anda network of sub-micron and non-sized pores. The pore size and structuremay be tailored, as needed, to provide a membrane 106 with desiredcharacteristics. HSA-CERCANAM® has been found to provide an effectivemembrane 106 to selectively remove hydrogen from the reaction zone 104and thereby drive the SMR and WGS reactions nearer to completion.

In selected embodiments, a wall 120 or surface 120 of the reaction zone104 may also be fabricated from HSA-CERCANAM®. This wall 120 may beinfiltrated or embedded with a catalyst material as previously discussedherein. The intrinsically high surface area of HSA-CERCANAM® improvesthe contact between the hydrocarbon feedstock and the catalyst, therebyimproving the yield of hydrogen gas in the product stream 108 comparedto other materials. This improvement in efficiency will be discussed inassociation with FIG. 9.

Although specific reference has been made herein to CERCANAM®, thereformer 100 is not limited these materials. Indeed, any reformer 100which utilizes a porous or ionically-conductive membrane 106 toselectively remove hydrogen from the reaction zone 104, while thereactions therein are occurring, is intended to fall within the scope ofthe invention. CERCANAM® or similar materials simply provide one exampleof materials that may be used to fabricate a reformer 100 in accordancewith the invention.

Referring to FIG. 2, in other embodiments, a microchannel reformer 100in accordance with the invention may be designed in a symmetricconfiguration to improve efficiency and generate additional product. Forexample, a microchannel reformer 100 may receive dual inputs streams 102a, 102 b, each containing a hydrocarbon feedstock fuel and steam. Thesestreams 102 a, 102 b may be conveyed to dual reaction zones 104 a, 104b, which may exist within microchannels of the device 100. A porousceramic membrane 106 a, 106 b may be placed adjacent to each reactionzone 104 a, 104 b. Each of these ceramic membranes 106 a, 106 b maycommunicate with a single product zone 107, which may output a productstream 108. Similarly, each of the reaction zones 104 a, 104 b maycommunicate with a different combustion zone 110 a, 110 b, whereresidual reactants and reaction products may be combusted to produceheat to drive the SMR and WGS reactions. By using dual reaction zones104 a, 104 b, more catalyst-infiltrated surface area is available toincrease the efficiency of the reactor 100.

Referring to FIG. 3, in selected embodiments, a catalytic microchannelreformer 100 in accordance with the invention may be scalable in orderto produce hydrogen at a desired rate. For example, in selectedembodiments, multiple microchannel reformers 100 a-d, each working inaccordance with the reformer 100 of FIG. 2, may be fabricated asinterconnectable modules 100 a-d. These modules 100 a-d may be linkedtogether to create a stack 300 having a desired hydrogen productionrate. Furthermore, modules 100 a-d may be added or removed from thestack 300, as needed, to increase or decrease the hydrogen productionrate.

Referring to FIG. 4, in selected embodiments, a microchannel reformermodule 100 may include one or more input ports 400 to receive an inputstream 102, namely a hydrocarbon feedstock fuel and steam. A centralproduct port 402 may output a product stream 108 containing hydrogen gasas the primary constituent. Exhaust ports 404 may be used to expel anexhaust stream 112 as well as supply air (i.e., oxygen) to an internalcombustion zone 110. As shown, in selected embodiments, the input ports400 and product port 402 may be located on a central interface plate406, allowing the ports 400, 402 to interface with corresponding ports400, 402 on adjacent modules 100 a-d.

Referring to FIG. 5, a cutaway perspective view of the microchannelreformer module 100 of FIG. 4 is illustrated. The module 100 includesinput streams 102, a product stream 108, and exhaust streams 112 to showthe flow of gases through the module 100. These streams 102, 108, 112may be compared to the schematic diagram of FIG. 2 to more fullyunderstand the flow and operation of the microchannel reformer 100. Asshown, ports are provided on a top and bottom side of the module 100 toallow the input stream 102 to flow to other downstream modules 100 aswell as receive a product stream 108 from downstream modules 100. Thereactions zones 104, combustion zones 110, and porous ceramic membranes106 a, 106 b are also shown within the device 100.

As explained previously, in selected embodiments, where CERCANAM® isused as the fabrication material, the module 100 may be fabricated in asfew as two processing steps, while understanding that the fabricationprocess is not limited to any specific number of steps. That is, theentire structure 100 may be fabricated in two casts, namely, one castfor the HSA-CERCANAM® portions and one cast for the LSA-CERCANAM®portions. Channels in the structure 100 may be formed by insertingsacrificial organic inserts into the CERCANAM® slip, such as mylar orplastic inserts. When the CERCANAM® structure is fired, these organicmaterials may burn away to leave the desired channels in the structure100.

Referring to FIG. 6, an alternative cutaway perspective view of themicrochannel reformer module 100 of FIG. 4 is illustrated. Like thecutaway view of FIG. 5, the module 100 is illustrated with the inputstream 102, product stream 108, and exhaust stream 112 to show the flowof gases through the module 100. The porous ceramic membranes 106 a, 106b and product zones 107 are also shown.

Referring to FIGS. 7 and 8, as mentioned in relation to Table I, thecombination of a higher initial concentration of H₂ in the reaction zoneand the higher diffusivity of H₂ compared to other gas species willresult in a product gas stream 108 with very high purity (e.g., greaterthan 91 percent hydrogen on a wet basis). We can carry this simplifiedcalculation a bit further by exploring the variation of the product gascomposition 108 as a function of the extent of reaction for eachreaction (i.e., the SMR and WGS reactions), while keeping the extent ofreaction for the other reaction constant. FIG. 7 shows the product gascomposition 108 as the extent of the SMR reaction goes from zero to fullcompletion. FIG. 8 shows the product gas composition 108 as the extentof the WGS reaction goes from zero to full completion.

As shown in FIG. 7, when the extent of the SMR reaction exceeds 0.6, theproduct gas composition is over 85 percent H₂, even where the extent ofthe WGS reaction is as low as 0.1. As shown in FIG. 8, where the extentof the SMR reaction is held constant, the H₂ concentration is only amild function of the extent of the WGS reaction. Thus, as long as theextent of the SMR reaction is 0.9 or higher, an H₂ concentration of over90 percent can be expected in the product gas stream 108.

The calculations provided in FIGS. 7 and 8 are based on a number ofsimplifying assumptions and thus should only be used as a guideline. Forexample, these calculations do not consider the thermodynamics of theSMR and WGS reactions. Furthermore, these calculations do not accountfor the fact that the reformer gas concentration may vary along thelength of the microchannels, resulting in variations in gasconcentration percolating across the channels at different locations inthe reformer 100. Furthermore, the extents of reaction are notindependent of each other. For example as the extent of the SMR reactionincreases, more CO and H₂ may be generated in the reactor 100. BecauseH₂ is removed from the reaction zone 104 much faster than CO, this wouldcreate an excess of reactants for the WGS reaction, thereby driving theequilibrium composition further towards the product side of thereaction. In addition, the selective removal of H₂ also drives the SMRreaction further towards the product side.

Other simplifying assumptions ignore other possible reactions that mayoccur in the reactor 100 such as “coking reactions” as indicated by thefollowing equations:CO+H₂→H₂O+CCH₄→2H₂+C

The first coking reaction is not favored in the presence of excess steamsince steam is on the product side of the reaction, and excess steamfavors the reverse reaction. On the other hand, too much steam in thefeed gas is also non-ideal since it reduces the overall efficiency ofthe microreactor due to the energy required to heat the excess steam.

Referring to FIG. 9, the difference in methane reforming capability forcatalysts embedded in different CERCANAM® materials is illustrated. Theupper curve 900 represents the extent of the SMR reaction where thecatalyst is infiltrated or embedded in a wall 120 made of HSA-CERCANAM®.The lower curve 902 represents the extent of the SMR reaction where thecatalyst is infiltrated or embedded in a wall 120 made of LSA-CERCANAM®.The graph shows that the extent of the SMR reaction was significantlybetter for HSA-CERCANAM® than it was for the LSA-CERCANAM® for allmeasured flow rates. These results show that the higher H₂ yields in theproduct gas stream 108 are likely due to the increased intimacy ofcontact between the catalyst and methane in the catalyst-infiltratedHSA-CERCANAM® wall 120.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed is:
 1. A method for enhancing the yield and purity ofhydrogen when reforming hydrocarbons, the method comprising: receiving ahydrocarbon feedstock fuel and steam at a reaction zone; reacting, atthe reaction zone, the hydrocarbon feedstock fuel and steam to producehydrogen gas; diffusing reactants and reaction products in the reactionzone through pores of a single layer ceramic porous membrane to aproduct zone, and selectively transporting hydrogen gas through thepores of the porous membrane from the reaction zone to the product zonewhile the reaction is occurring, wherein selectively transportingcomprises diffusing the hydrogen gas through the pores of the porousmembrane at a higher diffusion rate than diffusion rates of thereactants and other reaction products, and wherein a first surface ofthe single layer porous membrane is exposed to reaction zone and asecond surface of the single layer porous membrane opposite the firstsurface is exposed to the product zone; and conveying the reactants andthe reaction products that are not transported through the porousmembrane to a combustion zone.
 2. The method of claim 1, wherein thereaction zone and the product zone are in fluid communication throughthe pores of the porous membrane.
 3. The method of claim 2, wherein theporous ceramic membrane is fabricated from a mixture of alumina powderand a phosphate-containing reagent to react with the alumina powder. 4.The method of claim 1, wherein reacting the hydrocarbon feedstock fueland steam further comprises producing carbon monoxide at the reactionzone.
 5. The method of claim 4, further comprising reacting the carbonmonoxide with steam to produce hydrogen gas and carbon dioxide at thereaction zone.
 6. The method of claim 1, where selectively transportinghydrogen gas through the pores of the porous membrane further comprisesdiffusing, at a diffusion rate significantly lower than the diffusionrate of hydrogen gas, other gases through the pores of the porousmembrane.
 7. The method of claim 6, wherein the other gases comprise atleast one of carbon monoxide, carbon dioxide, steam, and gaseoushydrocarbon.
 8. The method of claim 1, further comprising providing heatto the reaction zone to aid in reacting the hydrocarbon feedstock fueland steam.
 9. The method of claim 8, further comprising combusting atleast one of residual hydrocarbon feedstock fuel, hydrogen gas, andcarbon monoxide in the combustion zone to provide the heat to thereaction zone.
 10. The method of claim 1, wherein the hydrocarbonfeedstock fuel is selected from the group consisting of methane,vaporized methanol, natural gas, vaporized diesel, and combinations andsub-components thereof.
 11. The method of claim 1, further comprisingcreating intimate contact between the hydrocarbon feedstock fuel, thesteam, and a catalyst while the reaction is occurring.
 12. A device forenhancing the yield and purity of hydrogen when reforming hydrocarbons,the device comprising: an inlet for receiving a hydrocarbon feedstockfuel and steam; a reaction zone in communication with the inlet to reactthe hydrocarbon feedstock fuel and the steam to produce hydrogen gas; asingle layer porous ceramic membrane in communication with the reactionzone to diffuse reactants and reaction products through pores of theporous ceramic membrane and to selectively transport hydrogen gasthrough the pores of the porous ceramic membrane out of the reactionzone while the reaction is occurring, thereby increasing the extent ofreaction between the hydrocarbon feedstock fuel and the steam, whereinthe selective transport of hydrogen gas comprises diffusion of thehydrogen gas through the pores of the porous ceramic membrane at ahigher diffusion rate than diffusion rates of the reactants and otherreaction products; a product zone to receive the hydrogen gastransported through the porous ceramic membrane, and wherein a firstsurface of the single layer porous membrane is exposed to reaction zoneand a second surface of the single layer porous membrane opposite thefirst surface is exposed to the product zone; and a combustion zone tocombust the reactants and the reaction products that are not transportedthrough the porous ceramic membrane.
 13. The device of claim 12, whereinthe porous ceramic membrane is fabricated from a mixture of aluminapowder and a phosphate-containing reagent to react with the aluminapowder.
 14. The device of claim 12, wherein the reaction zone is furtheradapted to react carbon monoxide with the steam to produce hydrogen gasand carbon dioxide.
 15. The device of claim 12, wherein the porousceramic membrane is further adapted to transport other gases out of thereaction zone at a diffusion rate significantly lower than the hydrogengas.
 16. The device of claim 15, wherein the other gases comprise atleast one of carbon monoxide, carbon dioxide, steam, and gaseoushydrocarbon.
 17. The device of claim 12, wherein the combustion zonecombusts at least one of residual hydrocarbon feedstock fuel, hydrogengas, and carbon monoxide to provide heat to the reaction zone.
 18. Thedevice of claim 12, wherein the hydrocarbon feedstock fuel is selectedfrom the group consisting of methane, vaporized methanol, natural gas,vaporized diesel, and combinations and sub-components thereof.
 19. Thedevice of claim 12, further comprising a porous ceramic layerinfiltrated with a catalyst adjacent to the reaction zone.
 20. A methodfor enhancing the yield and purity of hydrogen when reforminghydrocarbons, the method comprising: receiving a hydrocarbon feedstockfuel and steam at a reaction zone; reacting, at the reaction zone, thehydrocarbon feedstock fuel and steam to produce hydrogen gas; diffusingreactants and reaction products in the reaction zone through pores of asingle layer porous ceramic membrane, and selectively transportinghydrogen gas from the reaction zone to a product zone by extracting oneof hydrogen gas and hydrogen ions through a ceramic membrane while thereaction is occurring, wherein selectively transporting comprisesdiffusing the hydrogen gas through the pores of the porous membrane at ahigher diffusion rate than diffusion rates of the reactants and otherreaction products, and wherein a first surface of the single layerporous membrane is exposed to reaction zone and a second surface of thesingle layer porous membrane opposite the first surface is exposed tothe product zone; and conveying the reactants and the reaction productsthat are not transported through the porous ceramic membrane to acombustion zone.
 21. The method of claim 1, wherein the porous membraneis free of a discrete metallic layer.